Residual-type mask defect printability for extreme ultraviolet lithography

To evaluate the impact of residual-type mask defects on wafer printing during extreme ultraviolet lithography, a number of programmed residual-type defects were fabricated by etching line-bridging defects with full-height and with lateral dimensions of 900 × 225 nm in hp 225 nm line-and-space (L/S) patterns using electron beam (EB) induced gas-assisted etching (GAE). The heights of the fabricated defects were 33.1, 17.8, 8.2, and 2.9 nm, and after etching, no damage of any kind on the multilayer surface in the proximity of the etched area was observed using SEM and AFM. The wafer printability test was performed using an exposure tool with sufficient capabilities for resolving hp 45 nm L/S patterns. By analyzing the wafer printed images, the full etched defect was found to cause less than 0.6 nm of critical dimension (CD) change, which corresponded to 1.3% of CD error within a focus range of ±100 nm. This means that the EB induced GAE method can be considered quite suitable for the fabrication of residual-type programmed defects for wafer printability tests. The residual-type defects apparently did cause some CD errors on the wafer printed images, even where the residual-type defects happened to be only 8.2 nm high. The 33.1- and 17.8-nm-high residual-type defects caused line-bridging on the wafer printed images, whereas the 2.9-nm-high residual-type defect resulted in a 10% or higher CD error in the region outside the focus range.